The present invention relates to devices used for delivering a measured volume of powder from a hopper to an air stream, and more particularly pertains to a powder atomizer which can be combined with a feeder deagglomerator to deliver measured amounts of atomized powder into an air stream in the form of a moving particulate cloud.
In the past powders have been atomized in a number of ways. Hoppers have been used to feed powders to flowing air streams. Hoppers, however have been unsatisfactory in feeding powder because of the bridging of the powder or the electrostatic forces which are present between the particulate of the powder. The rate of flow can also be affected by such variables as humidity, particle size, particle shape, density, material cohesiveness, chemical composition, hopper configuration and electrostatic forces between the particulate powder. Additional problems are encountered when precisely measured amounts of powder need to be dispensed, at instantaneously uniform rates of flow and when the powder dispensed tends to agglomerate.
Therefore it is highly desirable to provide an improved powder atomizer, an improved powder feeder atomizer combination and an improved powder feeder atomizer deagglomerator combination. It is also highly desirable to provide an improved powder atomizer, an improved powder feeder atomizer combination and an improved powder feeder atomizer deagglomerator combination which can deliver precisely measured amounts of powder to controllably uniform flowing air streams.
Hoppers even when supplemented with vibrators are notoriously non-uniform in metering powder in precisely measured amounts in coating operations. Additional problems are encountered with coating wide substrates when powder fed by a hopper is attempted to be atomized into a flowing air stream inasmuch as the air used to atomize the powder is more or less two dimensional, i.e., longitudinally and in one lateral dimension. For wide web applications, this air stream is generally planar and of relatively low velocity. As such it does not apply the locally high velocity shear forces required to deagglomerate the powder from the feeder, and consequently, the cloud may include over sized agglomerated particles and heavy streams of non-uniform particulate concentrations which are undesirable in many processes. It is therefore highly desirable to provide an improved powder atomizer and an improved powder atomizer feeder combination and an improved powder atomizer feeder deagglomerator combination for wide web coating operations which can produce clouds of relatively uniform sized deagglomerated particulate material which are relatively uniform both transversely and longitudinal of the web.
Recently, accurately measured amounts of powder material can be metered into air streams and atomized utilizing material feeders such as disclosed in U.S. Pat. No. 5,314,090, and the size of the particulate in the cloud can be made more uniform by utilizing a deagglomerator such as disclosed in U.S. Pat. No. 5,035,364. While the combination of such a material feeder and deagglomerator is capable of producing uniform particulate clouds being uniform both in particulate size and distribution and both transversely and longitudinally of the cloud, the combination does not produce uniform clouds of particulate material in wide web applications such as powder coating of coiled metal sheets, and conveyors with closely grouped articles to be coated. The grouping of a plurality of material feeders and deagglomerator combinations side by side produces a cloud which may be uniform in particulate size longitudinally of the cloud flow. However, non-uniformity is still present transversely of the cloud because of overlapping and streaking. It is therefore highly desirable to produce an improved powder atomizer and powder atomizer feeder combination and an improved powder feeder deagglomerator atomizer combination which is capable of producing clouds of particulate material which are relatively uniform both longitudinally and transversely of the cloud and which contain particulate material of relatively uniform particulate size relatively uniformly distributed throughout the cloud over large areas such as encountered in wide web coating applications.
Recently, the precise metering of accurate amounts of powder can be accomplished utilizing the material feeder disclosed in U.S. Pat. No. 5,314,090 by utilizing an elongated brush which has an axial length larger than the width of the web being coated. Utilizing such an apparatus, accurate amounts of powder may be fed but not atomized or completely deagglomerated. Webs may be horizontally disposed and the top or bottom or both may need to be coated or may be vertically disposed and one or both sides may need to be coated. It is therefore highly desirable to provide an improved powder atomizer, an improved powder feeder atomizer deagglomerator combination and an improved powder atomizer feeder combination for use in both horizontal and vertical powder coating applications which produces a particulate cloud which is highly uniform in both transverse and longitudinal directions and in particulate size and particulate size distribution. It is also highly desirable to provide an improved powder atomizer, improved powder atomizer feeder combination and an improved powder feeder atomizer deagglomerator combination which can be utilized to direct a particulate cloud which is uniform both in transverse and longitudinal directions and both in particle size and particle size distribution to both the upper side of horizontally disposed webs located below the atomizer and the underside of horizontally disposed webs located over the atomizer or to the opposite sides of vertically disposed webs.
To provide uniformity and versatility, it is also highly desirable to provide an improved powder atomizer and an improved powder atomizer feeder combination and an improved atomizer feeder deagglomerator combination for such uses in a variety of applications at a reasonable cost.
Finally it is highly desirable to provide an improved powder atomizer, an improved powder atomizer feeder combination, and an improved powder feeder atomizer deagglomerator combination which has all of the above desired features.